In the conventional N-ary modulation (N is 2n, where n is an integer more than 1) employed in wireless communication, including satellite communication, digital micro-wave communication or mobile communication, it is customary to use modulation, with the N-ary value of 2n, n being a positive integer. Examples of this type of modulation include QPSK (quadrature phase shift keying), 8PSK (8-phase shift keying), 16QAM (16-quadrature amplitude modulation) and 64QAM.
In general, the N-ary value of 2n has been used by reason of circuit simplicity and compatibility with binary signal. However, with recent progress in the integrated circuit technology, implementation difficulties ascribable to complexity of the circuitry tend to be alleviated. On the other hand, the demand for more effective utilization of the frequency and the transmission power is increasing.
In order to meet the demand for more effective utilization of the frequency and the transmission power, 2n phase modulation is generally used as a modulation technique (see for example the Non-Patent Publication 1 below).
As the technique relevant to the present invention, reference may be made to the Patent Publications, indicated below. For example, in the Patent Publication 1, shown below, there is shown a general configuration of the modulation system in which binary signal are allocated to plural phase planes, a non-integer number of transmission bits is used per symbol.
In the Patent Publication 2, shown below, there is shown a configuration of the modulating system in which binary signal are allocated to plural phase planes, a non-integer number of transmission bits may be used per symbol and in which the physical array of signal points in the respective phase planes is of rotational symmetry of 90°. This application simply shows an arrangement of the physical array of 90° rotational symmetry of the signal points, while there is not disclosed the technique as to how the binary signal are allocated to the 90° rotational symmetrical signal points.
In the Patent Publication 3, similarly shown below, there is disclosed an n-ary modulation system in which (2p+1) columns of data signals is converted into two (p+1) columns of signals, which are then allocated to two phase planes, time-divisionally multiplexed and subjected to multi-value modulation to allow taking the number of the multi-level values on the order of 2(p+0.5). In the Patent Publication 4, shown below, there is disclosed an n-ary modulation system in which it is possible to take the number of the multi-level values on the order of 2(p+0.25) or 2(p+q/n). 
[Patent Publication 1]
JP Patent Kokai Publication JP-A-04-196945
[Patent Publication 2]
JP Patent Kokai Publication JP-A-04-196946
[Patent Publication 3]
JP Patent Kokai Publication JP-P2003-60724A
[Patent Publication 4]
JP Patent Kokai Publication JP-P2003-134184A
[Non-Patent Publication 1]
Yoichi Saitoh, ‘Modulation/Demodulation of Digital Wireless Communication’. Published in February 1996 by Society of Electronics Information and Communication
[Non-Patent Publication 2]
Noda, Nakamurand Koga, ‘Performance and Applications of PSK Modulation whose number of phases is not a power of 2’, ISITA2002, pp. 239-242, October 2002
[Non-Patent Publication 3]
ARIB-STD-28, Fourth Edition, 2002.3